Docosahexanoic acid-induced coronary arterial dilation: actions of 17S-hydroxy docosahexanoic acid on K+ channel activity.

Despite extensive studies, the mechanisms mediating the cardiovascular actions of ω-3 polyunsaturated fatty acids has not yet been fully understood. The present study determined the possible actions of an endothelium-derived lipoxygenase product of docosahexanoic acid (DHA), 17S-hydroxy DHA (17S-HDHA), in bovine coronary arteries. High-performance liquid chromatography (LC) analysis demonstrated that bovine coronary arterial endothelial cells can metabolize DHA via lipoxygenases, and one of the major products was confirmed to be 17S-HDHA by LC-tandem mass spectrometry. In isolated perfused small bovine coronary arteries, 17S-HDHA (10⁻⁹ to 10⁻⁵ M) caused a concentration-dependent dilation with a maximum dilator response of 87.8 ± 2.5%, which is much more potent than the dilator response of its precursor, DHA. Moreover, 17S-HDHA-induced vasodilatations were significantly blocked by iberiotoxin, a large conductance Ca²(+)-activated K(+) (BK(Ca)) channel blocker, but not altered by an ATP-sensitive K(+) channel blocker, glibenclamide. In patch-clamp whole-cell recording, 17S-HDHA markedly increased K(+) currents in coronary arterial smooth muscle cells. In the inside-out mode, but not in the cell-attached mode, 17S-HDHA dramatically increased the BK(Ca) channel activity, which was substantially blocked by iberiotoxin. Collectively, our findings indicate that 17S-HDHA, an endothelium-derived DHA product via lipoxygenase, activates BK(Ca) channels in coronary arterial smooth muscle cells, leading to coronary vasodilation, which may represent an important mechanism mediating the beneficial actions of DHA in coronary circulation.